Use /sys/class/net/<device>/carrier instead of operstate in is_up()

[itsfarseen]

When using android usb tethering in Arch Linux (kernel: Linux 5.6.5-zen4-1-zen),
operstate file shows unknown. But the carrier file correctly shows 1.
ethtool also correctly says Link detected: yes.

[ammgws]

It seems like there isn't 100% overlap between the two as operstate seems to offer some more context, but to be honest I'm not sure of the implications of losing that information. Unless you're sure that switching to just checking carrier is fine, perhaps we could check for both?

/sys/class/net/xxx/carrier

Indicates the current physical link state of the interface.
Posssible values are:
0: physical link is down
1: physical link is up

/sys/class/net/xxx/operstate

Indicates the interface RFC2863 operational state as a string.
Possible values are:
"unknown", "notpresent", "down", "lowerlayerdown", "testing",
"dormant", "up".

IF_OPER_UNKNOWN (0):
Interface is in unknown state, neither driver nor userspace has set
operational state. Interface must be considered for user data as
setting operational state has not been implemented in every driver.
IF_OPER_DOWN (2):
Interface is unable to transfer data on L1, f.e. ethernet is not
plugged or interface is ADMIN down.
IF_OPER_UP (6):
Interface is operational up and can be used.

https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-net
https://www.kernel.org/doc/Documentation/networking/operstates.txt

[atheriel]

I'd go with the official docs here and say we should check both. It's also a good idea to check the source of ethtool to figure out what it's doing here, if possible.

[itsfarseen]

Yeah it is a better idea to check both. I will re-add the code.
But by the way, I have been using this patch for a few days and it shows carrier file is not found error when I disconnect and reconnect the device. It only happens sometimes and goes away if I reload i3. This problem was not there when using operstate file.
What could be happening here?

[ammgws]

Seems like the file doesn't exist when the interface is down:
https://linuxconfig.org/how-to-detect-whether-a-physical-cable-is-connected-to-network-card-slot-on-linux

Checking both could be like:

1. check operstate
2. if not 'up', then check carrier
   3a. if carrier is 1 then return 'up'
   3b if carrier is 0/doesn't exist then return the original operstate result

[ammgws]

Ended up adding it myself. Thanks!